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FOREST RESEARCH NOTES
U.S.DEPARTMENT OF AGRICULTURE
CALIFORNIA FOREST AND RANGE
EXPERIMENT STATION *
STEPHEN N. WYCKOFF, Director
April 13, 1953
ANNOTATED LIST CF PINE HYBRIDS FADE
AT THE INSTITUTE OF FOREST GENETICS
By J. W. Duff ie Id and F. I. Righter
Fcrest Geneticists, California Forest and Range Experiment Station
Pine hybrids produced up to 194 at the Institute of Forest
Genetics were lasted in a recent publication to acquaint plant breeders
a-<xl botanists with the progress of the hybridisation wcrl< (7)i/.
Numerous requests for information about pine hybrids indicate that a
different type of publication on the pine hybridisation program is
needed; namely, a list of the hybrids by common names of their parental
species, giving a digest of our present knowledge obtained from results
of tests conducted at the Institute and elsewhere and our surmises
about the regions where the hybrids may be of value. This paper is
directed at that need.
Most plant hybrids can be expected tc be intermediate between
their parent species in most quantitative characters. Sometimes
hybrids resemble one parent in a certain character, such as resistance
to the pine reproduction weevil which the Jeffrey-Coulter pine hybrid
inherits from Coulter pine (A) . Less frequently, a hybrid may exceed
both parents in rate of growth or some other quantitative character.
This phenomenon is known as hybrid vigor. Even the truly intermediate
hybrid "may have some advantages. It may, for example, be able to
tolerate the adverse climate tc which its slower -growing parent is
adapted and in which its faster-growing parent cannot survive. Thus
almost any hybrid has potential value and merits at least small-scale
testing in the appropriate regions.
l/ Numbers in parentheses refer to bibliography at end of
* MAINTAINED AT BERKELEY, CALIFORNIA, IN COOPERATION WITH THE UNIVERSITY OF CALIFORNIA .
Agriculture — Berkeley
Suggestions given here on geographic and climatic adaptability
should he recognized merely as suggestions. They are often based not
on actual trials or careful studies of comparative climatology, but
on information about ' adaptation of pine species in various parts of
the world gleaned from the literature and from conversations with
visiting foresters from virtually every major coniferous forest
region of the world.
With regard to the availability of hybrid seed for testing or
large scale planting by others, some explanation of the Institute's
situation and policies is necessary. The Institute wishes to get
comprehensive information on the economic possibilities of the hybrids
which perform well at Placerville . This information would in the
future enable the Institute and other breeding agencies to breed for
specific purposes with greater precision than would otherwise be
possible. Such information can be obtained only from tests estab-
lished on suitable sites in various regions in the United States and
in foreign countries by cooperators having the knowledge, facilities,
and resources requisite for properly conducting the tests. This means
that the objectives and methods must be clearly understood and agreed
to in advance ; that the cooperator must have both control over the
area Involved and the personnel and means with which to maintain the
test and obtain the desired data on performance. As research insti-
tutions are best qualified in those respects, the Institute favors
them as cooperators; and accordingly most of its cooperative field
tests are being conducted by other Forest Service experiment stations
and by other research and educational institutions. Wood-using and
timber -growing industries and other private parties having the
requisite resources are welcomed as cooperators when seed is available.
No administrative procedure has been set up to enable the Institute to
make its products available for other than scientific purposes, except
to the U. S. Forest Service.
Unless otherwise stated, all tests so far made, have been con-
ducted at the Institute of Forest Genetics at Placerville, California,
latitude 39° north, longitude 121° west, altitude 2700 feet above sea
level. Temperature and precipitation data are as follows:
Temperature and Precipitation
Institute of Forest Genetics
: 1929-3 7
: Precipitation: Snowfall
: 1930-3' 7 : 1928-37
i / / n
> y • s
22. ' 7
The outstanding features of this climate are long dry summer, mild
rainy winter, and occasionally 20 inches or so of heavy, wet snow which
damages certain of the introduced pines. The soil at the Institute,
Aiken clay loam, has a rather high moisture -holding capacity, and despite
the long summer drought, moisture is available to tree roots in the lower
horizons. Pot culture tests have shown that the levels of available
phosphorus a^d nitrogen in Aiken clay loam are rather low. The conifers
growing spontaneously at the Institute are Pinus ponderosa Laws., P.
sab in! ana Dougl., P. lambertiana Dcugl., Ps eudotsv.ga taxif olie. (P ir.)
Britton, and Libocedrus decurrens Terr.
In the annotated list which follows, the name of the seed-parent
species is given first, the pollen parent second. English names are those
given in Standardized Plant Names Q) . The year-date which follows is
the year in which the cross was first successfully made at the Institute.
The list is not a complete catalogue of hybrids produced at the Institute
of Forest Genetics (hereafter abbreviated as IFG) — some hybrids unlikely
to have practical value are omitted.
1. KNOB CONE x MONTEREY (P. attenuata Lamm, x radiata D. Don). 1927.
Described as x P. atterjuradiata Stockwell and Righter (9).
Occurs spontaneously in Santa Cruz County, California. The cross
made at IFG utilized the economic ally -unimportant Sierra foothill
race of knobcone pine, which is more cold-resistant but less vigor-
ous than Monterey pine and the coastal forms of knobcone pine .
Hybrid is intermediate between the parents in growth-rate, cold-
resistance, stem-form, and flowering-time (9) .
Should be tested up to 3*000 feet on the west slope of the
Sierra Nevada against ponderosa pine, and its more promising
hybrids and against other commercially important species of forest
trees. At IFG the Monterey-knob cone hybrid appears to outgrow
ponderosa pine by at least 10 percent in height and diameter up
to 23 years (present age of oldest hybrids). Should also be
tested up to 3>000 feet in the Coast Ranges on ponderosa pine and
Douglas fir sites. Should be of value on colder margins of areas
where Monterey pine is grown successfully (e.g. Australia, New
Zealand, South Africa, Spain, Portugal, Chile, Argentine).
Wood tested at Forest Products ^Laboratory (i) was roughly
comparable to that of ponderosa pine in density and longitudinal
2. KNOBCONE x BISHOP (P. attenuata x muricata D. Don). 1946.
In early tests at IFG appears to outgrow both parents. Stem
form unknown. No recommendations for use can be made at present.
3. SHORE (closely related to lodgepole pine) x JACK (P.. ccntorta
Dougl . x banksiana Lamb . ) . ~ 194-6 .
In early tests at IFG outgrows shore pine and equals jack
pine. Depending on development of market for shore pine as source
of pulpwood, this may be of value in coastal Oregon, Washington,
and British Columbia; possibly also in British Isles, coastal
Norway, and Belgium. Stem form unknown.
4. LODGEPOLE x JACK (P. contorta var. latifolia Engelm. x banksiana ) .
Occurs spontaneously in Alberta (5.) . Described as x P.
mur r ayb ank s i ana Righter and Stockwell (6). In tests at IFG,
central Wisconsin, northern Idaho, and eastern Massachusetts, out-
grows California lodgepole in height and diameter. Early growth
about equal to that of jack pine, but in several localities, after
several years, the jack pine falls behind the hybrid. Produces
cones in third or fourth year. Should be valuable for pulpwood
production. Should be tested in Pacific Northwest, northern Rocky
Mountains, Lake States, northern New York, New England, and Ontario,
Quebec, and Maritime Provinces of Canada. Likewise in British
Isles, northern Europe, northeast Asia, and those parts of Australia
and New Zealand where lodgepole pine has been successful.
5. SANTA CRUZ ISLAND x MONTEREY (P. remorata Mason x radiata ) . 1942.
Grows at about the same rate as both parent species. Has
good form. This hybrid should be tested as a potential replacement
or alternative type wherever Monterey pine is used. Tests should
include resistance to insects such as Sirex noctilio , spider mites,
and other pests which, in certain localities, Impair the productivity
of Monterey pine.
6. JEFFREY x COULTER (P. jeffreyi Grev. & Balf. x coulter i D. Don).
Occurs spontaneously wherever parent species occur together.
In tests at IFG outgrows Jeffrey pine and is somewhat slower growing
than Coulter pine. So far, this cross has yielded very low propor-
tions of sound seeds. Therefore, the backcross hybrid listed below
is considered of greater practical importance.
7. JEFFREY x (JEFFREY-COULTER) (P. .jeffreyi x ( jeffreyi x coulteri ) ) .
Pollen from a natural hybrid (10) . Yields of seed of this
backcross are very high. Cage-tests at IFG suggest that this hybrid
is more resistant than Jeffrey pine to the pine reproduction weevil
which has caused high mortality in plantations of Jeffrey and ponderosa
pinefe in northern California. Preliminary results of uncaged tests
in 'localities in northern California, where the insect abounds, give
weight to the suggestion. The hybrids grow at approximately the same
rate as ponderosa pine, and have equally good stem form and branching
habits. In view of the susceptibility of ponderosa pine to the pine
reproduction weevil, these circumstances combine to make this back-
cress the most promising hybrid yet produced for use in the California
region. It is therefore being tested, under field conditions, through-
out the California pine region. It may not offer any advantage, however,
in comparison with ponderosa pine in regions not infested with the pine
8. PONDEROSA x APACHE (P. ponderosa x latifolia Sarg.).' 1943.
This hybrid outgrows both parent species, and is of great promise
for use in the California pine region, and perhaps in southwestern
U.S. and northern Mexico. It is susceptible to attacks of the pine
reproduction weevil but, due to its greater vigor, it outgrows suscep-
tibility to the insect more quickly than does ponderosa pine.
Nevertheless, steps are being taken to introduce reproduction weevil
resistance from Coulter pine.
9. PONDEROSA x ARIZONA (P. ponderosa x ponderosa var. arizonica
(Engelm.) Shaw). 1946.
This hybrid slightly outgrows ponderosa in height. Its early
performance in plantations at 6,000 feet on the Stanislaus National
Forest in California is excellent. It should be tested throughout
the California pine region, in southwestern U.S., and in northern
10. PONDEROSA x MONTEZUMAE (P. ponderosa x montezumae Lamb.). 1946.
In nursery tests at Placerville, this hybrid outgrows ponderosa
in height. It should be tested throughout the California pine region,
in southwestern U.S., and in northern Mexico.
11. COASTAL PONDEROSA x ROCKY MOUNTAIN PONDEROSA (P. ponderosa x ponderosa
var. scopulorum Engelm. ) . 1941.
The hybrid outgrows the Rocky Mountain variety and equals the
coastal and Sierra Nevada forms in tests at IFG. It may, therefore,
merit trial in the Rocky Mountain and Black Hills regions where its
cold -hardiness must be tested.
12. SHORTLEAF x SLASH (P. echinata Mill, x caribaea More let). 1931.
In tests at IFG appears to have narrower crown and finer
branches than shortleaf . Potential value seems to be in putting a
faster growing, better formed tree on shortleaf pine sites to the
north and west of natural distribution of slash pine. May prove to
have some value in developing a pine more resistant to fusiform
rusts than slash pine, in which case it may be of importance in the
general range of slash pine. Should be tested in areas to north
and west of natural distribution of slash pine.
13. SHORTLEAF x LOBLOLLY (P. echinata x taeda L. ) . 1933.
According to unpublished observations, occurs spontaneously
in east Texas and perhaps elsewhere. In tests at IFG outgrows
shortleaf in height and diameter by about 10 percent, and has shown
great resistance to cold in southern Illinois. May be of value on
shortleaf sites. Should be tested throughout natural distribution
of shortleaf pine.
14. PITCH x LOBLOLLY (P. rigida Mill, x taeda ). 1933-
This hybrid grows faster and has better form than pitch pine
but in tests in Maryland has seemed inferior to loblolly. It has
outgrown loblolly pine in New Jersey, and shortleaf pine in southern
Illinois where it appears to be more frost resistant than both lob-
lolly and shortleaf pine. It should be tested north of the distri-
bution range of loblolly pine in pitch pine areas, and in Illinois
where it may produce a tree of better form and faster growth than
pitch pine .
15. LOBLOLLY x SLASH (P. taeda x caribaea ) . 1931.
In small test at IFG, this hybrid appears to have somewhat
better form than loblolly. May be valuable in bringing a better-
formed, faster-growing tree into the loblolly region, and in
breeding a slash pine more resistant to fusiform rust. Should be
tested throughout the loblolly pine region.
16. SUGAR x ARMAND'S (P. lambertiana x armandi Branch. ). 1947.
Yields of seed following this cross are very low. Never-
theless, as Armand's pine is highly resistant to blister rust, this
hybrid may be of value in developing blister-rust-resistant sugar
pine. The first tests will be inoculation or exposure tests to
determine the degree of blister-rust resistance of this hybrid.
17. SUGAR x KOREAN (P. lambertiana x koraiensis Sieb . & Zucc). 1947.
This cross, likewise, is difficult to make; so far only one
seedling has been produced. As Korean pine is highly resistant to
blister rust, this hybrid should also be of value in developing
blister-rust-resistant sugar pine, and promises to be more cold
resistant than the sugar x Armand's hybrid.
18. WESTERN WHITE x EASTERN WHITE (P. monticola Dougl. x strobus L.).
This hybrid is of special interest because it has outgrown
both parent species In numerous tests made at IEG. Several geo-
graphic races of both parent species have been used in this cross,
always resulting in vigorous hybrids. Therefore, this hybrid should
be tested throughout the distribution ranges of both parent species.
The finding in both species of individuals which are apparently
resistant to blister rust (2_]_, (8), Inspires hope that vigorous
resistant hybrids will soon be produced.
19. WESTERN WHITE x HIMALAYAN WHITE (P. monticola x griffithi McClell.).
This hybrid outgrows western white pine and appears to be less
susceptible to blister rust than that species. The hybrid grows at
about the same rate as Himalayan white pine, but Is more drought
resistant. The hybrid should be tested throughout the distribution
range of western and eastern white pines, but may not be completely
cold hardy in the colder parts of these regions.
WESTERN WHITE x BALKAN WHITE (P. monticola x peuce Griseb.). 1947.
This hybrid grows no faster than western white pine but may
combine cold hardiness and moderate resistance to blister rust. Tests
of its susceptibility to blister rust must precede tests of its growth
in the field.
21. WESTERN WHITE x (BALKAN WHITE x EASTERN WHITE) (P. monticola x (peuce
x strobus ) ) . 1946.
This hybrid grows at about the same rate as the vigorous western
white x eastern white hybrid. Its value will depend on the outcome of
22. LIMBER x HIMALAYAN WHITE (P. flexilis James x griffithi ) . 1947.
In early test at IFG outgrows limber pine by 100 percent in
height. Should be of value as a blister-rust-resistant ornamental
white pine with greater cold resistance than Himalayan white pine.
Should be tested for both rust and cold resistance. Value as a timber
tree cannot yet be estimated, but its rate of growth is extremely
rapid for white pine .
23. EASTERN WHITE x HIMALAYAN WHITE (P. strobus x griffithi ). 1940.
This hybrid has shown good resistance to blister rust in a
rigorous exposure test in Oregon. It outgrows eastern white pine
and is about equal to Himalayan white and should be tested in the
distribution ranges of eastern and western white pines as well as
in those parts of Europe where the good growth of eastern white
pine is offset by its blister rust susceptibility.
Anderson, E. A. 1949. Specific gravity and shrinkage of Pinus
attenuata x radiata . Forest Products laboratory, Madison
Wisconsin. 7 p., 7 tables, 2 figs. (Typewritten report)
Bingham, R. T., A. E. Squillace, and J. W. Duffield. 1953.
Breeding blister-rust-resistant western white pine .
Jour. Forestry 51: 163-168.
Kelsey, H. P. and W. A. Dayton. 1942. Standardized plant names
Mc Far land, Harrisburg. 675 p.
Miller, J. M. 1950. Resistance of pine hybrids to the pine
reproduction weevil. California Forest and Range Exper-
iment Station. Research Note No. 68. 17 p.
Moss, E. H. 1949. Natural pine hybrids in Alberta, Canada.
Jour. Research, C. 27: 218-229.
Righter, F. I., and P. Stockwell. 1949. The fertile species
hybrid, Pinus murraybanksiana . Madrono 10: 65-69.
Righter, F. I. and J. W. Duffield. 1951. Interspecies hybrids
in pines. Jour. Heredity 42: 75-80.
Riker, A. J., T. F. Kouba, W. M. Brener, and L. E. Byam. 1943.
White pine selections tested for resistance to blister
rust. Jour. Forestry 41: 753-760.
Stockwell, W. P. and F. I. Righter. 1946. Pinus: the fertile
species hybrid between knobcone and Monterey pines.
Madrono 8: 157-160.
Zobel, B. J. 1951. The natural hybrid between Coulter and
Jeffrey pines. Evolution 5: 405-413.